I'm asking because it doesn't seem like fan-fold is available in Canada, probably because of the weather... anyways, I was wondering if it was the same material as the 2" pink insulation foam.
If it is, I could just make myself 3/8" panels out of a 2" sheet... I've done 1/2" already and they were perfectly straight...

The pink insulation foam, and the pink fan-fold are effectively identical. The fan-fold is pre sliced neatly into 1/4" thick sheets. The Blue fan-fold is really quite different. The foam is similar, but the fan-fold has a plastic skin on it that really adds to the stiffness and durability. That's the stuff to get if you can. Otherwise, spray the pink foam lightly with the old 3M-77 spray, and cover it with cheap packing tape to get the durability.